Micro-seismic imaging using source-independent waveform inversion

Using full waveform inversion (FWI) to locate microseismic and image microseismic events allows for an automatic process (free of picking) that utilizes the full wavefield. However, waveform inversion of microseismic events faces incredible nonlinearity due to the unknown source location and function (time). We develop a source independent FWI of microseismic events to invert for the source image and the velocity model. It is based on convolving reference traces with the observed and modeled data to mitigate the effect of an unknown source time. The adjoint-state method is used to derive the gradient for the source image and velocity updates. By inverting for both the sources image and the velocity model, the proposed method produces good estimates of the source location and the background velocity for part of the Marmousi model.